The present application relates generally to conductive interconnect structures, and more specifically to cobalt-based interconnect structures and capping layers that inhibit the oxidation and migration of cobalt.
Electrically-conductive connections between integrated circuit (IC) devices formed in a semiconductor substrate are traditionally made using multi-layer interconnects. Each interconnect layer can be supported over the substrate by an interlayer dielectric. Furthermore, electrical connections to and between different conductive layers are commonly made using contacts in the form of plugs that traverse one or more layers of the interlayer dielectric.
Typical interconnect structures comprise copper (Cu) or tungsten (W). Copper is advantageous because of its low electrical resistivity. However, copper is susceptible to electromigration and void formation, which can lead to device failure, while the precursors used during tungsten CVD processes are highly reactive with silicon and liner materials. Thus, tungsten is particularly sensitive to defects (e.g., pin-hole defects) in the barrier layer architecture used to isolate the tungsten interconnects from the liner metal and silicon. In addition, tungsten resistance cannot be decreased with post-deposition annealing as it is a refractory metal and does not undergo recrystallization or grain growth at thermal budgets that are compatible with semiconductor manufacturing. Moreover, the barrier and nucleation layer thicknesses for tungsten-based metallization are not scaling to meet resistance requirements at advanced nodes.
An alternative interconnect material to copper and tungsten is cobalt. Due to a higher activation energy, cobalt is less prone to electromigration compared to copper, and is compatible with thin barrier layer architectures, which can be especially advantageous at advanced nodes, e.g., less than 14 nm. Processing subsequent to the formation of cobalt contacts, however, including the deposition of an overlying interlayer dielectric, can induce unwanted oxidation, diffusion and/or migration of cobalt. Cobalt oxidation can undesirably increase contact resistance. Migration of cobalt can lead to electrical shorts between adjacent structures, which can adversely affect device performance and reliability.
Various approaches to capping cobalt contacts, including the capping of cobalt contacts with dielectric materials such as silicon oxynitride, have been shown to be ineffective at inhibiting cobalt migration. For instance, FIG. 1A is a cross-sectional micrograph showing a plurality of comparative cobalt contacts 40 embedded within an interlayer dielectric 20 with a dielectric capping layer 50 formed over the contacts 40. FIG. 1B is an elemental line scan across the highlighted region of FIG. 1A showing the undesired migration of cobalt to regions of the structure between adjacent contacts following formation of a dielectric capping layer over the interlayer dielectric layer.